#include <stdio.h>
int main(void)
{
    int grade;
    printf("Enter numerical grade: ");
    scanf("%d", &grade);
    if (grade > 100 || grade < 0) {
        printf("Wrong grade !\n");
        return 1;
    }
    grade /= 10;
    switch (grade) {
    case 9: case 10:
        printf("Letter grade: A\n");
        break;
    case 8:
        printf("Letter grade: B\n");
        break;
    case 7:
        printf("Letter grade: C\n");
        break;
    case 6:
        printf("Letter grade: D\n");
        break;
    case 0: case 1: case 2: case 3: case 4: case 5: 
        printf("Letter grade: F\n");
        break;
    default:
        printf("Wrong grade !\n");
        return 1;
    }
    return 0;
}